Field of the Invention
The present invention relates to the technical field of lighting devices, in particular to the technical field of lighting devices for road illumination.
State of the Art
Lighting assemblies for road applications belonging to the state of the art and commonly available on the market generally comprise: a main body adapted to provide the whole structure with mechanical support and equipped with the appropriate hooking and securing means on poles, cables, spans, chains and walls; a light source (generally with filament or discharge) provided with corresponding mechanical securing and connection and power supply means; a possible reflector adapted to convey the light emission of said light source to a space portion and optics generally comprising a diffuser consisting of a transparent or semi-transparent screen, adapted to close the main body and, possibly, filter the emitted light according to the desired modes.
The road illumination has some peculiarities related to the reflection features of the road surface, which is in general anisotropic. The light reflection occurs according to the angles of light incidence and reflection on the road surface, and therefore, in order to optimize the road lighting and avoid dangerous shadow areas, the light emission is to be directed where it is more effective, i.e. in directions where the luminance result is higher and more uniform.
In essence, the light emission is to be directed to the road surface areas where the ratio of the resulting luminance with the illumination is higher so as to achieve better illumination results using less light emission, and in the areas where the resulting luminance is more uniform, so as to comply with the uniformity requirements set forth in the regulations in force.
In the case of LED lighting assemblies, the overall light emission flow may be directed in a more accurate and exact manner, as each LED may be adjusted in order to conveniently direct the emitted light flow thereof.
In the State-of-the-Art apparatuses, the single LEDs are generally arranged on the same plane and the light is to be diverted in the desired directions so as to obtain the desired overall light beam.
For this purpose, TIR (Total Internal Reflection) lenses, associated with each single LED, are usually employed.
From a point of view, if using single TIR lenses ensures a high level of flexibility, on the other implies a range of technical problems. Firstly, as said TIR lenses are normally made of plastic material, problems related to the natural decay of the material features may occur. In facet, yellowing and matting of the employed plastic materials may occur in a relatively short time and heavily affect the apparatus performance.
Also, using TIR lenses in lighting assemblies for road illumination makes very difficult directing the light emission accurately enough to avoid the lights from being dispersed in the areas close to the area to be illuminate, thus damaging the energy saving of the system. In fact, evaluating and controlling the useful portion of the flow is quite important, which portion is the apparatus flow fraction effectively sent to the area to be illuminated and provides direct information on the amount of light which is sent by the considered lighting apparatus to the concerned area and outside it. The light flow percentage sent to undesired areas is a drop of the energetic performance of the lighting device and therefore, ultimately, a waste of energy to be avoided or, at least, limited.
Lastly, according to the Law of Optics related to the refraction phenomenon, when a light radiation passes from a material to another (as in the passages between air and plastics and then between plastics and air), a decay in intensity and quality of the emitted light beam occurs. Sometimes, in case of white light emission, phenomena of light decomposition into the coloured components may arise, due to refraction.
So as to solve the above-described technical problems, it is therefore apparent the need for lighting apparatuses adapted to optimize their illumination profile without compromising an efficient management of the power dissipated by the employed light sources.